Since on-chip routers in Network-on-Chips play a key role in on-chip communication between cores, they should be always preparing for packet injections even if a part of cores are in standby mode, resulting in a larger standby power of routers compared with cores. The run-time power gating of individual channels in a router is one of attractive solutions to reduce the standby power of chip without affecting the on-chip communication. However, a state transition between sleep and active mode incurs the performance penalty, and turning a power switch on or off dissipates the overhead energy, which means a short-term sleep adversely increases the power consumption. In this paper, we propose a sleep control method based on look-ahead routing that detects the arrival of packets two hops ahead, so as to hide the wake-up delay and reduce the short-term sleeps of channels. Simulation results using real application traces show that the proposed method conceals the wake-up delay of less than five cycles, and more leakage power can be saved compared with the original naive method.